1. Field of the Invention
The present invention relates to a secondary battery, and more particularly, to a gasket structure for a secondary battery which may enhance the gas or fluid tightness of the battery.
2. Description of the Related Art
Unlike a conventional primary battery, a conventional secondary battery may be recharged. Lower power batteries in which one battery cell is made into a battery pack are used as the power source for various portable electronic devices such as cellular phones, laptop computers, and camcorders. Bulk size batteries which are formed by connecting plural secondary battery cells serially or in parallel may be suitable as the power source for electric vehicles.
Depending on their external shape, secondary batteries may be classified into different types, for example, square and cylindrical batteries.
Conventional secondary batteries include an electrode assembly in which a positive electrode and a negative electrode of a long belt shape, and a separator as an insulator interposed therebetween, are spirally-wound. The electrode assembly is inserted inside a container, and a cap assembly is mounted on the container to form the battery.
The cap assembly seals the opening of the container to maintain the inner gas or fluid tightness of the container. For cylindrical batteries, when the cap assembly is coupled with the container, a separate gasket is interposed between the cap assembly and the container to maintain the inner tightness. However, a gap between the cap assembly and the container is created in spite of the gasket, thereby decreasing the tightness of the secondary battery.
That is, when the cap assembly is inserted into the container through the gasket and assembled with the container by a clamping process, since the surface of the conventional gasket contacting the container and the cap assembly has a flat shape, the tightness is poor.
Especially if the gasket is not uniformly pressed during the clamping process of the container, the gasket may become irregularly distorted so that some portions of the gasket do not contact the container or the cap assembly, thereby widening the gap.
In addition, for square batteries, when a flat gasket is disposed between the cap plate and the external terminal, the gasket may unevenly contact the adjacent member to create a gap.